2025 version based on fabric 6.5.4 (typescript) and @VitaliiBratok answer:

import { Point } from 'fabric';

const transformedPoints: Point[] = polygon
      .get('points')
      .map((p: Point) => {
        return new Point(p.x - polygon.pathOffset.x, p.y - polygon.pathOffset.y);
      })
      .map((p: Point) => {
        return p.transform(polygon.calcTransformMatrix());
      });